The invention concerns a refrigerated display case and its use, having at least one unit composed of a plurality of wall assemblies, namely a bottom assembly, a rear wall assembly, and a top assembly, which delimit a cooling space at the bottom, the rear, and the top, and having a cooling unit whose components include at least one evaporator, one condenser, and one electric control unit.
In modern refrigerator units, there is increased interest in replacing widely used conventional (generally fluorinated) refrigerants with environmentally friendlier so-called natural refrigerants. One such suitable replacement, for example, is carbon dioxide, but its use is accompanied by a significant equipment expense. In addition, hydrocarbons such as propane or butane have turned out to be well-suited for use as refrigerants, particularly because of their low greenhouse potential, good availability, and advantageous thermodynamic properties for a refrigerant.
But hydrocarbons have a high ignitability so that when they are used as refrigerants, restrictive regulations apply with regard to safety requirements (e.g. IEC 600335-2-89). Thus with a capacity of greater than 150 g of hydrocarbon refrigerant per refrigerant circuit, particularly in enclosed spaces, the safety requirements rise significantly so that significant expense must be incurred to meet these requirements. There is thus a need for development, particularly for required total quantities of greater than 150 g in a refrigerator unit, in order to be able to efficiently use hydrocarbons as environmentally friendly refrigerants.
AT 504 774 A1 has disclosed a refrigerator and freezer unit with a refrigeration machine, which is operated with a natural working substance such as propane or ammonia; in a heat exchanger circuit, C02 circulates as a heat transfer medium. For personal protection, this document proposes placing the heat exchanger circuits that are operated with C02 inside the space with the refrigerated display cabinet or wall rack and placing the refrigeration machine separate from this, outside of this space.
The ILK Dresden document: Propane as a Refrigerant in Small Refrigerant Circuits [Propan als Kältemittel in Kleinkältekreisläufen], URL: http:IIwww.ilk dresden.de, describes the development of a mini-channel evaporator in connection with heat pump-clothes dryers, the objective being to minimize the refrigerant capacity to a maximum of 150 g. It should be noted that the use in embodiments with evaporators is difficult.
In DD 2 66 153 D1, a refrigeration unit particularly intended for refrigerated vehicles is disclosed, which has two or more separate refrigerant circuits with shared evaporators and condensers, the objective being to ensure an emergency operation, but also to avoid an oil displacement. The use of and problems in connection with natural refrigerants are not addressed in detail.
Examples for general structures of refrigerated display cases are shown in DE 10 2012 107 713 A1 and DE 20 2014 100 665 U1. Conventional refrigerants are used in refrigerated display cases of this kind.